Aircraft pilots continuously face the threat of colliding with “targets” such as ground vehicles, stationary ground-based objects, and other aircraft. Therefore, aircraft cockpits often contain a Cockpit Display of Traffic Information (CDTI) for displaying, on the CDTI's display screen, icons that represent relevant targets and useful information about these targets. Such information may include, for example, the altitude, heading, and identification of each target displayed on the CDTI. The CDTI may receive this target-related information from a surveillance system that receives the information from one or more sources, such as the Traffic Information Service (TIS) (which is broadcast from a ground system) and from various Automatic Dependent Surveillance-Broadcast (ADS-B) signals, which are broadcast from transponders mounted within various targets.
CDTI systems help pilots avoid collisions by displaying any targets that may pose an immediate threat of colliding with the pilots' aircraft. When using a CDTI system, a pilot monitors the CDTI display to determine whether there is any immediate danger that his aircraft will collide with a target shown on the CDTI display. If so, the pilot uses the information displayed on the CDTI to visually locate the threatening target, and to avoid colliding with the target.
In order to help pilots quickly identify targets that pose an immediate threat to their aircraft, it is desirable to provide a CDTI display that filters from display any targets that do not pose a relatively immediate threat to the aircraft. This allows pilots to focus their attention on only truly threatening targets. Accordingly, some prior systems include a horizontal range filter to filter targets from display on the CDTI based on the horizontal distance between the aircraft containing the CDTI (i.e. the “Own Ship” 0 Aircraft) and the various targets detected by the system. For example, a pilot using one of these prior art CDTI's might specify that the CDTI should not display any targets that are more than 10 horizontal miles from the Own Ship. Thus, if the system were to detect a particular target that is 15 miles in front of the Own Ship, the CDTI would not display the target.
Some prior art systems also allow pilots to filter targets from display on the CDTI based upon the altitude of the target. For example, some prior art systems are configured to filter from display any targets that either: (1) have an altitude that is greater than a fixed, pre-determined upper altitude (e.g. 5000 feet above the “Own Ship” aircraft); or (2) have an altitude that is less than a fixed, pre-determined lower altitude (e.g. 5000 feet below the Own Ship aircraft). In addition, some prior art systems allow a pilot to operate the CDTI in three different modes of operation. These modes of operation include lookup mode, look-down mode, and look level mode.
In look-up mode, the fixed, pre-determined upper altitude is generally farther away from the Own Ship aircraft than the fixed, pre-determined lower altitude. For example, the fixed, pre-determined upper altitude might be 5000 feet above the Own Ship aircraft and the fixed, pre-determined lower altitude might be 2000 feet below the Own Ship aircraft. Such a configuration is useful when the Own Ship aircraft is ascending and, therefore, is at a greater risk of colliding with targets above the Own Ship aircraft than below the Own Ship aircraft.
In look-down mode, the fixed, pre-determined lower altitude is generally farther away from the Own Ship aircraft than the fixed, pre-determined upper altitude. For example, the fixed, pre-determined upper altitude might be 2000 feet above the Own Ship aircraft and the fixed, pre-determined lower altitude might be 5000 feet below the Own Ship aircraft. Such a configuration is useful when the Own Ship aircraft is descending and, therefore, is at a greater risk of colliding with targets below the Own Ship aircraft than above the Own Ship aircraft.
In look-level mode, the fixed, predetermined upper altitude is generally about the same distance from the Own Ship aircraft as the fixed, pre-determined lower altitude. For example, the fixed, pre-determined upper altitude might be 5000 feet above the Own Ship aircraft and the fixed, pre-determined lower altitude might be 5000 feet below the Own Ship aircraft. Such a configuration is useful when the Own Ship aircraft is flying relatively level so that the risk of colliding with targets above the Own Ship aircraft is similar to the risk of colliding to the risk of colliding with targets below the Own Ship aircraft.
One disadvantage of prior art CDTI systems is that they are only capable of filtering aircraft from display based on fixed, pre-determined altitude thresholds. Thus, for example, when operating in look-level mode, such systems may only be capable of filtering from display any targets that have an altitude that is either: (1) greater than a fixed pre-determined upper altitude of 5000 feet above the Own Ship aircraft; or (2) less than a fixed pre-determined lower altitude of 5000 feet below the Own Ship aircraft.
In some situations, however, it may be desirable to filter targets based on different upper and lower threshold altitudes than those fixed by the system. For example, if the Own Ship aircraft is flying level in a very crowded area, the pilot may wish to focus his attention on targets that are very close to the Own Ship aircraft. Thus, for example, the pilot may wish to specify that the system should filter from display any targets that are greater than 3000 feet above the Own Ship aircraft, or that are less than 3000 feet below the Own Ship aircraft. This would not be possible when using a prior art system, such as the system described above, in which the CDTI system is configured to always have an upper threshold altitude of 5000 feet above the Own Ship aircraft, and a lower threshold altitude of 5000 feet below the Own Ship aircraft when the system is in “look-level” mode.
Similarly, if the same aircraft is flying level in an uncrowded area, the pilot may wish to monitor all aircraft that are in the general vicinity of the Own Ship aircraft. In such a case, the pilot might wish to specify, for example, that the system should only filter from display any targets that are greater than 24,500 feet above the Own Ship aircraft and 24,500 feet below the Own Ship aircraft. This would also not be possible using the prior art system described above.
Thus, there is a need for a CDTI system that is capable of filtering targets based on threshold altitudes that may be adjusted to account for different flying environments.